As shown in FIG. 9, VCRs have mounted on a chassis 1 a rotary head cylinder 11 incorporating a rotary magnetic head (not shown) and a pair of reel supports 12, 13 for rotatingly driving the reels of a tape cassette 9. The chassis 1 is formed at opposite sides of the cylinder 11 with a pair of guide slits 14, 15 having slidably fitted therein a pair of leading guides 16, 17 for winding the magnetic tape 91 of the cassette 9 around the rotary head cylinder 11. Further disposed at the right side of the cylinder 11 is a tape drawing-out lever 10 pivotally supported so as to be movable between a tape drawing-out start position and a tape drawing-out end position and provided with a pin 10a for drawing out the magnetic tape 91 from the cassette 9.
An unillustrated drive control mechanism drivingly advances the leading guides 16, 17 and pivotally moves the lever 10 from the drawing-out start position indicated in solid lines to the drawing-out end position indicated in chain lines, whereby the magnetic tape 91 is positioned along a specified path of travel under tension. The tape as held between a capstan 18 and a pinch roller 19 is driven longitudinally thereof by the rotation of the capstan 18.
FIG. 8 shows a tape drawing-out mechanism previously developed by the present applicant.
Disposed on the rear side of the chassis is a drive control plate 4 to be reciprocatingly driven by a motor (not shown). A tape drawing-out lever 2 is supported at its base end by a first pivot 20 on the chassis. A drive lever 3 is supported at its base end by a second pivot 30. The lever 2 has an outer end carrying a pin 21 for drawing out the tape and a driven gear portion 22 formed at its base end. The drive lever 3 has a forward end formed with a drive gear portion 31 always in mesh with the driven gear portion 22 of the lever 2. The drive lever 3 has a cam follower 32 projecting downward from an intermediate portion thereof and extending through the chassis to engage in a cam groove 41 formed in the drive control plate 4.
With the tape drawing-out mechanism described, the control plate 4 rotates counterclockwise, thereby causing the cam groove 41 to drive the cam follower 32 of the drive lever 3 and rotate the drive lever 3 clockwise. With this rotation, the drive gear portion 31 of the drive lever 3 drivingly rotates the driven gear portion 22 of the tape drawing-out lever 2 clockwise, moving the lever 2 from the tape drawing-out start position to the illustrated tape drawing-out end position. As a result, the magnetic tape is drawn out of the tape cassette and positioned along the specified path under tension.
In the tape drawing-out mechanism shown in FIG. 8, the force F exerted by the tension of the magnetic tape on the tape drawing-out pin 21 on the lever 2 is first amplified to a reaction P shown in accordance with the ratio between the radius L of gyration of the pin 21 and the radius K of pitch circle of the driven gear portion 22. The force Q exerted by this reaction P on the drive gear portion 31 is amplified to a reaction R shown and acting on the cam follower 32, at a ratio determined by the radius C of pitch circle of the drive gear portion 31 and the radius D of gyration of the cam follower 32. The reaction R is about 10 to about 20 times the original force F, and the cam face defining the cam groove 41 is pressed by this amplified reaction R.
Consequently, the cam face defining the cam groove 41 wears away early, presenting the problem that the pin 21 fails to draw out the tape to an accurate position.